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8.2 CA WITH LICENSED ASSISTED ACCESSThe main goal for LTE in unlicensed spectrum is to leverage the relatively large amount of unlicensedspectrum in order to provide better mobile service. Given the transmit power restrictions imposed onunlicensed bands, it is expected to be primarily deployed in small cells. No standards exist for LTE inunlicensed spectrum and the various technical and regulatory items need to be addressed in the future.However, the mobile industry is discussing certain technical proposals which include an LTE carrier inunlicensed spectrum (as a secondary LTE cell) combined with an LTE carrier in licensed spectrum (as theprimary LTE cell) using CA, with all control channels on the licensed spectrum LTE carrier.The LTE carrier on the unlicensed spectrum can either be a Supplemental Downlink (SDL) or can beused for DL and UL transmissions. Due to the tight combination of licensed and unlicensed carriers anddue to control channels being on the licensed primary cell, the technology is also called LicensedAssisted Access. Specifically, industry proposals do not describe “stand-alone” LTE in an unlicensedspectrum system where there is no LTE carrier. A key technical requirement and benefit targeted bythese proposals is to extend the management, QoS mechanisms 13 , security and mobility aspects of LTEinto the unlicensed spectrum. These benefits are the key reasons brought forth by proponents.The primary targeted unlicensed band is the 5 GHz band. However, the regulations for usage of this bandvary across the world and standards will have to account for them. The industry proposals describe theneed for Wi-Fi co-existence and articulate how the two unlicensed technologies may complement eachother. It cannot be overstated that LTE in unlicensed spectrum can only be a supplementary technologyto LTE, which today is operable only in licensed spectrum. Specifically, development (and deployment) ofLTE in unlicensed spectrum does not decrease the need for additional licensed spectrum because highquality services with high predictability can only be provided via the usage of licensed spectrum.Most industry proposals describe using LTE in a CA or SDL implementation in which LTE in theunlicensed band operates in conjunction with LTE in the licensed band. There have been some industryproposals for a “stand-alone” mode of operation, in which LTE operates in unlicensed spectrum withoutthe need for LTE in licensed spectrum.Figure 26. Unified LTE Network for both Licensed and Unlicensed Spectrum [16].13 It should be noted that services requiring QoS levels other than best efforts would typically not be transmitted over unlicensedspectrum due to the lack of predictability4G Americas LTE Carrier Aggregation October 2014 45